3.3.4 Southern reliefs

Natural vegetation and the rest by agriculture occupy 70% of this rolling area. According to the data collected during the fieldwork and the interpretation of the satellite images, five major areas of natural vegetation were distinguished, according to the prevalence of:

• artificial forest;
• Quercus suber;
• Tetraclinis articulata;
• mediterranean shrubs,
• low shrubs.

In the Northern part afforestation prevails over the natural forest mainly composed by Quercus suber and Tetraclinis articulata.

The cork oak is present as sparse trees, mixed with the species used for afforestation or with Mediterranean shrubs, but it becomes more abundant in the South, where no afforestation is present. Comparing Landsat images of 1985 and 2000, it is evident that afforestation has been carried out on eroded areas, derived from the degradation of the Quercus suber forest. This is a common task for all the cork oak forests, due to intense grazing that causes scarcity in variety and density of species.

On the other hand, the Tetraclinis articulata is rarer than in the North, probably because it is more strictly linked to the sloping areas. It is sparse and present only in the eastern part.

The species used for afforestation is mainly Pinus halepensis, but also Eucalyptus camaldulensis and Eucalyptus gomphocephala. The oldest afforestation was carried out about 25 years ago and all the species were planted without taking the slopes or aspects into consideration; the only discernible criteria could have been that eucalyptus was planted more closely to agricultural and urban areas. Generally these zones are difficult to reach so, probably, the only aim of these plantations was soil conservation, restoration, and fuelwood for local people. Usually the artificial forest is not on the summit of the hills but on the slopes, where the trees have been planted on terraces along the contour lines. Much of this kind of afforestation failed.

The undergrowth can be of two types: the first one composed by medium to high shrubs as Phillirea latifolia, Pistacia lentiscus, and Olea europaea var. oleaster, the second one composed by low and closed shrubs of Cistus monspeliensis. On the top of the hills the soil can be bare with presence of erosion, especially gully, or covered by low and open shrubs as Cistus spp., Pistacia lentiscus, and Olea europaea var. oleaster (Table 24). In the valleys along the oueds, or where water is seasonally present, there is a higher and denser vegetation composed by Pistacia lentiscus, Olea europaea var. oleaster, Phillirea latifolia, Arbutus unedo, Myrtus communis, and Tamarix gallica (Table 25).

With respect to aridity, pine and eucalyptus are both suitable for this area, as water is not a very strong limiting factor for them. The minimum annual rainfall they can face is 400-300mm, so they well suit the local value. In spite of the suitability of these species for drought-resistance, many new plantations have failed; this could be due to the severe aridity occurred during the past four years in all North Africa. Pinus halepensis can grow in every kind of soil, even in the less favourable ones, while eucalyptus needs deep soils and is not very suitable for calcareous ones, especially the E. camaldulensis. This requirement can probably explain the poor results of the eucalyptus plantations in this area and the good ones in the northern part.

The regeneration of the Aleppo pine is strictly affected by the presence of undergrowth, because it needs light to grow, and by the possibility of recolonization and growth of either the oak forest or the matorral of Pistacia and Olea. So, if the purpose is to maintain this kind of forest, there should be a undergrowth control to let the regeneration grow. If the purpose is to restore the cork oak forest, it could be useful to exploit pine cover to establish the natural forest, for example sowing together oak and pine seeds or supporting the regeneration already present. Anyway it is impossible to plan forest renovation or enrichment without a grazing control, especially for goats.

In the South afforestation becomes rarer and Quercus suber forest prevails restoring the original formation of these hills. The density of the trees is open, about 30%, while on the top of the hills and on the steeper slopes, they become sparse until there are only isolated trees (see relevés 102, 211, 420, and 421 in Table 22).

The undergrowth is mainly composed of Cistus monspeliensis creating a sort of carpet under the trees; this is the formation that shows the degradation of cork oak forest and it is due to intense grazing. Undergrowth can also be composed by of Mediterranean shrubs that become more frequent and abundant in the valleys, along the river, on the slopes facing North, or in the steeper area. In these zones the shrubs are higher and denser. On the tops of the hills the shrubs are lower as well as vegetation cover.

Another degradation factor is the setting up of agriculture in former forest surfaces along the North border.

Another important formation of the southern hills is the Tetraclinis articulata. It covers a wide surface in the central part of the rolling area. Locally the Tetraclinis is able to grow in a flat area, as is usual for this species, but the soil is superficial, rocky, and calcareous. The formation is a monospecific and coppice forest. The cover is about 60% and the undergrowth is rare, low, and intensely grazed. There does not seem to be any kind of programmed management but there is wood collection, probably done only by local people, mainly for tool making.

In the western part of the rolling area there is a big zone totally covered by low and sparse shrubs: respectively Chamaerops humilis in the northern part and Cistus salvifolius in the southern part. It is a sloping area, especially in the South and the soil is rocky. Agriculture is absent because of the presence of hard materials and the lack of soil formation. The stony soil is not the only reason for the poverty of this part but probabily also animal grazing, which is the only souce of the income of this area.